a) Field of the Invention
The invention relates to an arrangement for examination of vision functions, and, in particular, an arrangement for the subjective determination of refraction in the eye.
b) Description of the Related Art
There are various known spectacle type or helmet type frames which arrange screens in front of the eye of the observer or which reflect the image generated by screens or displays in front of the eye of the observer: U.S. Pat. Nos. 5,076,275, 4,361,384, 5,162,828, U.S. 4,869,575, Enhanced Vision. "V-max", brochure 800-440-9476, 1996. "Virtual displays" of this kind are sold by Virtual Research Systems, Inc. (FAG), for example.
U.S. Pat. No. 5,369,415 and EP 562,742 describe "direct retinal scan displays" in which only very low outputs (not more than 20 micro watts) are required owing to direct "writing" of the image information on the fundus oculi of the observer. Video information (e.g., RGB signals) is modulated on one or more laser beams and the latter is/are deflected in the x-direction and y-direction via scanners (e.g., piezo-crystals) and reflected into the observer's eye via a plane surface which can be spectacle glass. Variable optics serve to focus the beams on the retina.
U.S. Pat. No. 5,467,104 and WO 94/09472 describe a "virtual retina display" with high resolution and color representation. Light from lasers or LEDs is modulated, transmitted via light guides, and projected directly onto the retina by means of microscanners and projection optics. The reflecting element can also be a splitter mirror, so that the projected image is superimposed on the surroundings.
In WO 96/17562, a scanning unit is provided on a spectacle type frame and projects an image onto the retina via the reflecting spectacle lenses or glasses.
A "pupil tracking system" monitors the position of the eyes and displaces the projection direction so as always to strike the pupil of the observer. In DE 4091126, the patient views a screen through spectacles with liquid crystal shutters, on which screen are displayed symbols for binocular vision testing.
DE 4326760 C2 describes a device for testing central vision functions, preferably for perimetric examinations, wherein a light-proof or light-tight spectacle type carrier contains image-generating display screens for generating test marks or optotypes and an optical imaging system for compensation of refractive anomalies. The natural visual impression is impaired by the part of the spectacles arranged in front of the eyes which has screens in the viewing direction.
Examination instruments such as phoropters in which, e.g., spherical or cylindrical test glasses are swiveled in front of the eye to determine defective eyesight based on information from the test subject are known for determining subjective refraction and for determining other functions of the human eye. A disadvantage herein is that the test subject does not assume a relaxed posture and the natural visual impression is corrupted.
Therefore, arrangements have been developed to enable so-called "free-vision" refractive testing (U.S. Pat. No. 3,927,933, DE 2647848 A1, DD 293045 B5, DD 282851 B5, DD 273771 A1).
Further, test equipment for determining other functions of the human eye are known (OCULU.S.-Binoptometer, Binotest) to acquire information on the visual performance (e.g., color vision, stereo vision, driving vision) of the patient's eyes based on information given by the patient. These arrangements also have the disadvantage that they take up a relatively large amount of space and are poorly suited for mobile use, e.g., in developing countries. When used for testing defective vision of persons, especially for the first time, the test subject will often exhibit objective shyness of the medical equipment, which makes the examination difficult or even impossible.